Does he atleast have a good punish into command grab to build sun stacks?
He has some VERY good punishes. Kotal is, generally speaking, an awesome punisher. He has high damaging punishes starting with 114 (his fastest and most damaging punisher starter), F1B2, and F2
that can ALL be ended with command grab to level up your grab each time you punish your opponent. So, punishes and building sun stacks is not Sun God's problem.
The problem with both Sun God and Blood God is basically what regulas just wrote: Both variations have very limited options to open people up and are severely lacking in mix-ups . Blood God is designed to compensate for this by using his totems to inflict a ridiculous amount of damage and to take less damage than anyone else on the roster. Sun God is designed to compensate for this by punishing people for blocking his limited mix-ups with his command grab. The problem I see for Sun God, however, is that the command grab just isn't that good. It's a 13 frame startup (not terrible, but not great), its range is decent (but again, not great) and its damage is meh. Maybe I am spoiled from maining Bane, but I just don't think Sun God's command grab is quite as good as it should be. Having made my reservations about Sun God abundantly clear, I think he is hella fun to play and you should definitely check him out if you like command grabs.